Lesion of the striatal DA afferent projections leads to a significant decrease of spine density on dendrites belonging to the three types of MSNs. The overall spine density was 4.0 ± 0.4 spines/10 μm in 6-OHDA compared to 6.4 ± 0.3 in sham (P < 0.0001) for the D1 MSNs; 5.1 ± 0.3 spines/10 μm compared to 6.6 ± 0.2 (P = 0.0018) for the D2 MSNs and 3.0 ± 0.1 spines/10 μm compared to 4.0 ± 0.2 (P = 0.0427) for the D1/D2 MSNs. These reductions accounted for a 37.5% loss on the D1, 22.7% on the D2 and 25.0% on the D1/D2 MSNs. The Sholl analysis indicates that such lower spine density is maintained throughout the entire dendritic arborization of the three types of MSNs (Fig. 7).
